1. Field of the Invention
The present invention relates to an ethanol fuel reforming system for an internal combustion engine bringing an ethanol fuel used for an internal combustion engine into contact with a catalyst to reform ethanol into diethyl ether.
2. Description of the Related Art
In recent years, in order to reduce the fuel consumption of internal combustion engines per predetermined load and predetermined time, and to reduce the amount of emission matters from internal combustion engines, compression ignition internal combustion engines represented by homogeneous charge compression ignition internal combustion engines have been under review. In the compression ignition internal combustion engine, oxygen containing gas and a compression ignition fuel are introduced into the cylinder and compressed to ignite the fuel spontaneously.
However, as distinct from spark ignition internal combustion engines, the compression ignition internal combustion engines have a difficulty in controlling the ignition timing. In the compression ignition internal combustion engines, use of a fuel with high ignitability tends to cause knocking when a high load is required for the engines, and use of a fuel with low ignitability tends to cause misfire when a low load is required for the engines. Thus the compression ignition internal combustion engines have a problem of having a narrow operating range where the engines can be operated safely.
In order to overcome the problems, there is conventionally known a technique of mixing two fuels of a highly ignitable fuel and a less ignitable fuel and providing the mixed fuel to compression ignition internal combustion engines depending on required load. However, application of the technique makes mounting the compression ignition internal combustion engines on automobiles and the like complex, because the technique requires two fuel tanks and fuel-by-fuel supply.
Then there is investigated that a part of one fuel is reformed to obtain two fuels with different ignitability. Such a fuel to be reformed is, for example, an ethanol fuel such as gasoline containing ethanol. A technique is suggested that ethanol contained in the ethanol fuel is reformed into diethyl ether (see Japanese Patent Laid-Open No. 2006-226172).
Ethanol can be easily reformed into diethyl ether by heating ethanol to about 200° C. with an acid catalyst. The technique uses gasoline containing ethanol as a first fuel and ethanol is reformed into diethyl ether by bringing a part of the first fuel into contact with an acid catalyst contained in a reformer and heating the first fuel and the catalyst.
As a result, gasoline containing diethyl ether as a second fuel is obtained. Diethyl ether has higher ignitability than ethanol, and the first fuel has low ignitability and the second fuel has high ignitability.
The compression ignition internal combustion engines are regarded as having an enlarged operating range where the engines can be operated safely, by increasing the ratio of the first fuel under high load and increasing the ratio of the second fuel under low load in mixing the first fuel with low ignitability and the second fuel with high ignitability and providing the mixed fuel to the engines.
However, there is a disadvantage that the reaction of reforming ethanol into diethyl ether is difficult to maintain with stability because the reaction tends to be influenced by heating temperature.